The present invention relates to a data terminal device for communicating digitally coded information through an information distribution network such as a telephone network.
A data terminal device communicates digitally coded information according to a predetermined protocol which defines the band ratio, the bit number of the data and so on. If a protocol, which defines the format of the data, is transmitted from a data terminal device in a transmitting mode, and is different from a protocol of a data terminal device in a receiving mode, the digitally coded data communication cannot be maintained between the data terminal device in the transmitting mode and the data terminal device in the receiving mode.
Therefore, the protocol of the data which is transmitted by the data terminal device in the transmitting mode, should coincide with the protocol of the data terminal device in the receiving mode. To correspond both protocols with each other, the data terminal device in the transmitting mode transmits an initial signal which indicates a protocol defining the format of the data following the initial signal. However, if a data terminal device in a receiving mode fails to receive the initial signal because of noise or other interruptions, data communication cannot be maintained.